Patent GB-1308084-A (GB)
Title: Method and apparatus for making anhydrous magnesium chloride
IPC: C01C1/16
Filed: 1970-12-23
Abstract: 1308084 Magnesium chloride J G MACEY 23 Dec 1970 [29 Dec 1969] 61213/70 Heading C1A Anhydrous purified magnesium chloride is produced by (a) decomposing the ammonium carnallite in a decomposition zone to ammonium chloride vapour and molten magnesium chloride in the absence of metal and contaminants while maintaining a positive pressure of ammonium chloride vapour in the zone, (b) recirculating the molten magnesium chloride between the decomposition zone and a superheating zone and maintaining at least a portion of the molten magnesium chloride in the superheating zone in excess of the melting point of the magnesium chloride, whereby magnesium chloride recirculated from the superheating zone to the decomposition zone provides necessary heat for decomposing the ammonium carnallite, (c) passing at least a portion of the molten magnesium chloride into a heated holding zone and maintaining the magnesium chloride in the zone at a low enough temperature above the melting point thereof to inhibit turbulence of the magnesium chloride and to allow precipitation of any calcium oxide therein, and (d) removing purified molten magnesium chloride form the holding zone and separately recovering ammonium chloride vapour from the decomposition zone. As shown in the Figure apparatus for decomposition of ammonium carnallite and recovery of purified magnesium chloride comprises (a) a ceramic lined decomposition chamber 14 containing a metal-free decomposition area 12 sealed from contaminants, the chamber including a jacketed ammonium chloride gas exit conduit 34 disposed in the upper portion thereof, (b) a screw-type feeder line 16 connected to the upper portion of the chamber and adapted to pass hot particulate ammonium carnallite into the chamber while minimizing entry of contaminants including oxygen and water vapour into the chamber, (c) a super-heating chamber 66 comprising a heatconductive container 72 adapted to pass heat into contact with the interior thereof, (d) means to pass molten magnesium chloride between the decomposition chamber and the super-heating chamber, (e) a holding chamber 90 comprising a heat-conductive shell and means for maintaining the temperature of magnesium chloride just above the melting point thereof, (f) means to pass molten magnesium chloride from the superheating chamber to the holding chamber, and (g) means for recovery of ammonium chloride from the holding chamber. Super-heating chamber 66 comprises an outer ceramic shell 70 and a metallic shell 72 spaced inwardly therefrom and connected therewith to provide a heating space 74 for direct gas flame firing. The decomposition furnace 14 comprises an outer ceramic shell 18, an inner ceramic shell 20 spaced inwardly therefrom and connected thereto to define a heating space 26, a steel liner 22 connected to the outer surface of the inner shell, the upper portion of each of the shells being domed. A lower free-end 30 of domed portion 28 extends below the surface of the molten magnesium disposed within an area 32 defined by shell 20 to prevent escape of ammonium chloride vapour from the furnace 14 except through conduit 34. The exit conduit 34 preferably comprises a monel metal supply line connected to ammonium chloride recovery means 40 which comprises a gas absorber having revolving drums 46 disposed to intercept the water level in reservoir 44 so as to generate a fine spray of water droplets, an aqueous ammonium chloride solution exit line 58, an exhaust gas exit line 53 and a fresh water supply line 56. The means for recovery of ammonium chloride from the holding chamber may comprise moulds 92 and a dip tank 94 for coating the solidified moulded magnesium chloride with a moisture-proof peelable skin coating.